Return correct type from dbe_alloc in error(EEXISTS) case

In timing situations where a port-create is in-flight and
another for same name is received, when check for dup is
false in http_post_common but caught in dbe_alloc, the return
type in dbe_alloc was incorrect causing incorrect further
processing.

Change-Id: I34edf4d61c1edc9071da154747ff7066aeefef92
Closes-Bug: #1382385
Merge "Return correct type from dbe_alloc in error(EEXISTS) case"